Electric dialing circuit



NOV. 1954 w. SIX ETAL ELECTRIC DIALING CIRCUIT Filed May 1, 1952 I/VVENTORS J wibllemD Sixb oco us 9 w lawr United States Patent Ofifice 2,693,503 Patented Nov. 2, 1954 ELECTRIC DIALING CIRCUIT Willem Six and Jacobus Domburg, Eindhoven, Netherlands, assignors to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application May 1, 1952, Serial No. 285,408

Claims priority, application Netherlands May 23, 1951 8 Claims. (Cl. 179-16) This invention relates to electronic dialling circuits for automatic signalling systems, for example, telephone systerns, for the numerical establishment of a connection be tween one of a plurality of apparatus of a first kind, for example a connecting circuit, and one of a plurality of apparatus of a second kind, for example a subscribers line circuit or a subsequent dialling stage, each having associated with it a number or a figure.

A circuit has been suggested, in which such a connection may be established with the use of gas-filled discharge tubes, for example, cold cathode tubes. In this circuit a multipled point of each apparatus of the first kind is connected by way of an impedance to a first terminal of a source of supply and also coupled by way of a discharge path of a gaseous tube to a multipled point of each apparatus of the second kind. Each multipled point t is connected by way of an impedance to a second terminal of the source of supply. The difference in potential between the terminals of the source of supply is smaller than the ignition voltage of the discharge paths, but greater than the operating voltage. made of a marking circuit for receiving dialling signals transmitted by a subscriber, an input control-point of said marking circuit being connected to the multipled point of the apparatus of the first kind, which point may have supplied to it dialling pulses. A plurality of marking output points are coupled to ignition electrodes of the gaseous tubes, which are connected to the multipled point of the apparatus of the first kind. The voltage of the marking point connected to the ignition electrodes of the gaseous tube associated with an apparatus of the second kind corresponding to the number is increased as a function of the number dialled to such extent that the gaseous tube concerned may become conductive if the apparatus is free, that is to say, if none of the other gaseous tubes connected to the multipled point of the said apparatus is conductive. However, the gaseous tube cannot become conductive if the apparatus is busy, since in this case the voltage of the multipled point differs from the voltage of the second terminal of the source of supply and is active at at least one of the electrodes of the gaseous tube, for

example the ignition electrode or the cathode, in such manner that the ignition voltage cannot be exceeded.

As a rule, it is desirable in such dialling circuits that it should be possible to utilize an electronic counting circuit, for example a counting circuit comprising gaseous tubes or an electron-beam counting tube, as a marking switch. In this case the difficulty arises that steps must be taken to avoid undesired ignition of a gaseous tube during a series of dialling pulses or upon occurrence of pulses at the multipled point of the apparatus of the first kind due, for example, to the extinction or ignition of a gaseous tube or to a call being answered.

The object of the invention is to avoid the above-described drawbacks and to provide an improved elec- Provision is also I) a gas-filled tube to a common point P of each of a plurality of connecting circuits. For the sake of simplicity, the figure shows only three subscribers stations AA, AB, AC with the associated line current paths LCA, LCB, LCC and a single connecting circuit VC. The line current paths of lines which are not shown, are exactly similar to the line circuits LCA, LCB, LCC, whilst the coupling of the subscribers station AA, AB, AC with connecting circuits which are not shown is eifected in a manner exactly similar to the coupling with the connecting circuit VC.

Each subscribers station AA, AB, AC is connected across two primary windings of a transformer TA, TB, TC, respectively, the junction between the two primary windings of a transformer being by way of a source of supply V2. One of the extremities of a secondary winding of TA, TB, TC is connected to earth by way of a parallel combination of a resistor Rm, R11), R10 and a capacitor Cm, C11,, Cm, respectively. The otherextremity of the secondary winding is connected to the cathode k of the gaseous tube BA, BB, BC, through which the line is coupled to the connecting circuit VC. The cathodes of gaseous tubes (not shown) by which the lines are coupled to the other connecting circuits, are connected in a similar manner to the multipled points A, B, C of the line circuits. The anode a of the tube BA, BB, BC is connected to the common point P in the connecting circuit VC, which point is connected by way of an inductor L1 and the parallel combination of resistor R1 and capacitor C1 to the point of supply V1, the potential of which is higher than the operating voltage of the gas-filled tube BA, BB, BC, but lower than the ignition voltage between cathode k and anode a. The ignition voltage is for example, 170 volts and the operating voltage is 60 volts. The voltage V1 may then, for example, be 140 volts. Each gas-filled tube BA, BB, BC, comprises two ignition electrodes f1 and f2. The ignition voltage between the ignition electrodes f1 or f2 and the cathode of a tube is 70 volts. The ignition electrodes f1 are connected to tappings on high-ohmic voltage dividers R421, R5a, and R41), R b and R46, Rsc, respectively, which are included between a junction point Q, between inductor L1 and resistor R1, and supply source V7, such that the difference in potential between each ignition electrode f1 and the associated cathode k is slightly lower than the ignition voltage, if none of the tubes BA, BB, BC connected to point P is conductive. The normal voltage of the ignition electrodes fl is, for example, 80 volts. The normal voltage of the ignition electrodes f2 is equal to earth ,potential and hence much lower than the normal voltage of the ignition electrodes f1.

The tubes BA, BB, BC may serve to establish a connection between a calling line and a connecting circuit and also for the numerical establishment of a connection between the connecting circuit and a calling line.

It is assumed that the subscriber at station AA having the number 2 wants to establish a connection with the subscriber at station AB having the number 3. When the subscriber at station AA lifts his handset, the line loop is closed through the apparatus at station AA, so that a strong negative voltage pulse is produced across the secondary winding of transformer TA. While only one tube BA is shown connected to point A, it is to be understood that a plurality of like tubes BA may be connected to point A. The voltage difference between the ignition electrodes f1 and the cathodes k of the tubes BA, which couple the station AA to free connecting circuits, thus exceeds the ignition voltage, so that all the tubes BA can become conductive. The ignition electrodes h of tubes BA, which couple the multipled point A to busy connecting circuits VC, have a lower potential, since the potential of the points Q of the said connecting circuits is lower than that of V1, which prevents the tubes from being ignited. As soon as one of the tubes BA starts to become conductive, the main discharge path between the cathode k and the anode a of this tube BA also ignites, so that current starts to flow from the supply point V1 by way of resistor R1, inductor L1, common point P, discharge path between anode a and cathode k of the tube BA, multipled point A, secondary winding of transformer TA, and resistor Rm to earth. A voltage drop thus occurs across the resistors R12, R1, so that the potential of the rnultipled point A increases by 40 volts and the potential of the point Q decreases by 40 volts. The increase in the potential of point A results in the difference in potential between the cathode k and the ignition electrode f1 of the tubes BA becoming smaller than the ignition voltage, so that the said other tubes cannot ignite. Consequently, one tube BA only is ignited.

Due to the decrease in the potential of point Q, the potential of the ignition electrode f1 of the tubes which couple the connecting circuits to other subscribers lines also decreases. Consequently, it is avoided that upon a subsequent call by one of the other subscribers, one of the said tubes could ignite and this subscriber could also engage the connecting circuit VC, in other words the connecting circuit is marked busy by the decrease in the potential of point Q.

The subscriber AA subsequently dials the desired number, in this case the figure 3. The subscribers dial is shunted by an impedance (not shown). With each dialing pulse the line loop is interrupted incompletely, so that the pulses which occur, during dialling, across the primary winding of transformer TA are smaller than the pulses which occur across the primary winding by closing or opening the line loop when the telephone is removed or replaced. Dut to the diiferentiating action of transformer TA, a positive pulse occurs at the beginning of each dialling pulse and a negative pulse occurs at point A at the end of each dialling pulse. The amplitude of said pulses is approximately volts. The pulses are transferred by way of the discharge path between cathode k and anode a of tube BA and inductor L1 to the point Q and thence transferred by way of a capacitor C9 to the control grid of a vacuum amplifying tube B1, by which said pulses are amplified and supplied with opposite polarity to a point U. The cathode of tube B1 is connected to earth by way of a resistor R3, the anode being supplied by way of resistor R2 from the source of supply V1. With each dialling pulse, transient positive and negative pulses of comparatively small amplitudes thus occur successively at the point U. The negative pulse has no effect. The positive pulse is supplied by way of capacitor C2 to the ignition electrode 1 of a gasfilled discharge tube B4, which electrode is connected by way of resistor R4 to a source of supply V3, the voltage of which is such that the gaseous tube B4 becomes conductive if a small positive pulse is supplied to the point U. The positive pulse at the point U is furthermore supplied by way of capacitor C3 and resistor R5 to the ignition electrode 7 of a gas-filled discharge tube B5, which ignition electrode is coupled by way of resistor R6 to a source of supply V4, the voltage of which is so much lower than that of the source of supply V3 that the tube B5 can ignite only with a much stronger positive pulse at the point U. Consequently, tube Bs does not ignite upon reception of dialling pulses.

The anode a of tube B4 is connected to the source of supply V1. The gaseous tube B4 becomes conductive with the first dialling pulse. The cathode of this tube is connected to earth by way of an impedance Z4, constituted by an inductor in series with a resistor shunted by a capacitor. The elements of said impedance are chosen to be such that the gaseous tube B4 cannot operate in a stable manner, but extinguishes again immediately after ignition. Similar impedances Z2, Z3, Z5 are included for the same purpose in the cathode leads of the gas-filled discharge tubes B2, B3, B5.

When tube B4 becomes conductive, a positive pulse occurs at the cathode k of this tube, which pulse is transferred by Way of capacitors C11, C12, C13, C111 to the ignition electrodes 1'' of the gas-filled discharge tubes B11, B12, B13, Bin of an electronic counting circuit MS of a kind known per se, which constitutes part of the VC.

The anodes a of the tubes B11, B12, B13, Bln are connected to the source of supply V1, the cathodes It being connected by way of resistors R11, R12, R13, R1 to a common point W, which is connected to earth by way of a resistor R33. The ignition electrode 1 of tubes B11 is connected to a tapping point on a voltage divider R31, R32, included between earth and the source of supply V1. The cathodes k of the tubes B11, B12, B13, Bin are coupled by capacitors C21, C22 etc. Furthermore, the ignition electrodes 1 of the tubes B12, B13 etc. are connected by way of resistors R21, R22 etc. to the cathode of the preceding tube. The gaseous tubes are cut off in the normal condition of the circuit, the control electrode f of tube B11 having a potential higher than that of the ignition electrodes of the other tubes.

Since the tube B4 becomes conductive with each dialling pulse, a positive voltage pulse is supplied to the ignition electrode of all gaseous tubes 1311 etc. of the counting circuit MS. Since the ignition electrode of tube B11 has a normal potential higher than that of the other ignition electrodes, B11 only ignites. The voltage of the ignition electrodes of the other tubes remains below the ignition voltage. Consequently, a current starts to flow from the source of supply V1 by way of the discharge path between anode a and cathode k of tube B11 and by way of resistor R33 to earth, so that the potential of the point W increases and the difference in potential between the ignition electrode and the cathode of tube B11 decreases. The potential of the ignition electrode of tube B12 increases more than the potential of the cathode due to the voltage drop across the resistor R11.

After the first dialling pulse, the tube B11 only has become conductive and tube B12 is prepared for subsequent ignition. The tube B12 does not ignite with the first dialling pulse, since upon an increase in the potential of the cathode of tube B11 a positive voltage pulse is supplied to both the cathode of tube B12 by way of capacitor C21 and to the ignition electrode of tube E12 by way of resistor R21, said pulsess counteracting one another.

With the second dialling pulse, the tube B4 becomes conductive for the second time and supplies a second positive pulse by way of capacitors C11, C12, C13 etc. to the ignition electrodes 7 of all gaseous tubes of the counting circuit MS. Since the ignition electrode of tube B12, as a result of the increase in potential of the cathode of tube B11, now has the highest potential of the ignition electrodes of the counting tubes, the gaseous tube B12 becomes conducting with the second counting pulse, with the result that the potential of the cathode k of tube B12 increases. Now, a positive voltage pulse is transferred by way of capacitor C21 to the cathode k of tube 811, so that this tube extinguishes. After the second dialling pulse, the ignition electrode f of tube B12 has the highest potential of the ignition electrodes, since this ignition electrode is coupled by way of resistor R22 to the cathode of tube B12, so that tube B13 is now prepared for subsequent ignition. Similarly, with the third dialling pulse, tube B13 is ignited and tube B12 extinguishes.

Consequently, tube B11 is conductive after one dialing pulse, tube B12 is conductive after two dialling pulses, tube B12 is conductive after two dialling pulses, tube B13 after three dialling pulses, etc. Each tube thus corresponds to a determined figure. Each ignition electrode f2 of the tubes BA, BB, etc. is coupled by way of an integrating network constituted by resistors Rza, R32 and capacitors C22, C321 and resistors R21), R31: and capacitors C211, Cab etc. respectively, to the cathode of the tube of the counting circuit MS which numerically corresponds to the number of the line with which the tube BA or BB is associated. Thus, for example, the ignition electrode 2 of tube BB, which corresponds to the subscribers station AB and which has associated with it the number 3 is coupled to the oathode of tube B13, which is ignited after three dialling pulses. Similarly, the ignition electrodes f2 of the tubes BC and BA, which correspond to subscribers stations having associated with them, the numbers 1 and 2 are coupled to the cathodes of the tubes B11 and B12 respectively.

If one of the tubes B11, B12, etc. of the counting circuit is conductive, the voltage of the point W and hence the voltage of the cathodes of the other tubes is 40 volts. This voltage is lower than the ignition voltage between ignition electrodes 1 and cathode k of the tubes BA, BB, BC. The voltage of the cathode of the conductive tube is 80 volts and hence higher than the said ignition voltage.

With the first dialling pulse, the tube B11 ignites and the voltage of its cathode increases to 80 volts. Tube BC does not ignite, however, since the voltage of the ignition electrode f2 cannot suddenly change to 80 volts, but can increase only comparatively slowly as a result of the integrating action of the network RZc,

C211, R30, Gas. With the second dialling pulse, the tube B11 extinguishes and the voltage of its cathode decreases to 40 volts. Thus, the voltage of the ignition electrode f2 of tube BC cannot reach the ignition value (70 volts). With the third dialling pulse, the tube B13 ignites, so that the voltage of the ignition electrode f2 of gaseous tubeBB increases. Since the third dialling pulse is not followed by further pulses, the voltage of electrode f2 can assume a value such that the tube BB becomes conductive, if the subscriber at station AB is not busy.

Assume now that the station AB is busy. One of the tubes (not shown), of which the cathodes are connected to the point B, is then in a conductive condition, so that the voltage 01' point B is either 40 volts or 27 volts, according to whether the subscriber at station AB is dialling or is otherwise busy. When the voltage of the ignition electrode f2 of tube BB has increased to 80 volts, only a voltage of 40 volts or 53 volts, i. e. a voltage lower than the ignition voltage, is set up between the ignition electrode f2 and the cathode k, so that tube BB cannot ignite.

The subscriber at station AA then receives busy tone.

'A tapping point S on the inductor L1 is connected by way of capacitor C8 and a rectifier g1 to one extremity of a winding of a transformer TG, the other extremity of which is connected to a source of supply Vs, the voltage of whichis 20 volts. Another winding of transformer TGis connected to a common busy-tone generator GB. The junction between capacitor C3 and rectifier g1 is connected bywayof resistor R34 to the point W. So long as the counting circuit MS is in its normal position, the voltage of the point W is equal to earth potential and rectifier g1 is cut off. However, if one of the tubes ofthe counting circuit MS is conductive, the voltage of point W is 40 volts and rectifier g is conductive. The generator GB then supplies busy tone to subscriber AA by way of rectifier g1, capacitor C8, inductor L1, tube BA and transformer TA.

When the subscriber at station AA, after his call has not been answered, replaces his receiver, a strong positive pulse is produced in the secondary winding of the transformer TA due to the line loop being opened. As a rule, this closing pulse is of such strength that the tube BA extinguishes, so that a strong positive pulse occurs at points Q. If, for example, as a result of a high resistance of the line, the pulses at point A were not sufiiciently strong to extinguish the tube immediately, the tube transfers the pulse to point Q, so that even in this case a strong positive pulse occurs at point Q. The closing pulse is transferred by tube B1 with opposite polarity to the point U and thence transferred by way of a capacitor C5 and a rectifier g2 to the oathode of tube B3. The ignition electrode f of tube B3 is connected to a source V5 of a voltage such that tube B3 ignites if a strong negative pulse such, for example, as occurs when the receiver is replaced, is supplied to the cathode, but cannot become conductive with a comparatively weak pulse such, for example, as occurs with a dialling signal. When tube B ignites, the voltage of the cathode greatly increases and a strong positive pulse is supplied by way of a capacitor C6 to the ignition electrode 1 of tube B2, which ignition electrode is connected by way of resistor Rs to a source Vs of a voltage such that tube B2 becomes conductive. Consequently, the potential of the anode a of this tube decreases and a strong negative pulse is supplied by way of a capacitor C7 and inductor L1 to the anode a of tube BA, as a result of which this tube extinguishes, if it had not already been extinguished immediately by the pulse at the point A. Furthermore, due to the ignition of tube 133, a strong positive pulse is supplied by way of rectifier g2 and capacitor C5 to the point U and thence transferred by way of capacitor C2, to the ignition electrode 1 of tube B4 and by way of capacitor C3 and resistor R5 to the ignition electrode 1 of tube B5. The tubes B4 and B5 are thus ignited. Tube B4 ignites somewhat later than tube B5, since the pulse to the ignition electrode of tube B5 is somewhat retarded by the presence of the network R5, C4. The ignition of tube B41 causes a subsequent tube in the counting circuit MS to become conductive in the manner which has already been described. However, a tube which couples point P to another subscribers line cannot thus ignite, since tube B5 also becomes conductive a short time after tube B4. The ignition of tube B5 results in a strong positive pulse at point W, by which the voltage of the cathode of the conductive tube in the counting circuit is suddenly increased to such extent that this tube ex tinguishes and the counting circuit MS is returned to its normal position. The tubes B2, B3, B4, B5 re-extingalish automatically after their ignition due to the presence of the impedances Z2, Z3, Z4, Z5 in their cathode leads. All gas-filled tubes are thus extinguished and the circuit is returned to its normal position.

As mentioned before, the potential of point Q decreases by 40 volts when subscriber AA is calling due to the tube BA becoming conductive. Consequently, tube B supplies a strong positive pulse to the point U, so that tube B2 ignites and, furthermore, tube B11 in the counting circuit MS becomes conductive, similarly as with reception of the first dialing pulse. However, the positive pulse at point U is now of such strength that the tube B5 ignites, due to which tube B11 immediately extinguishes again, as described above. The rectifier g2 prevents the positive pulse at the point U from being transferred to the ignition electrode f of tube B2. The pulse which occurs at point Q upon calling, in contradistinction to dialling pulses, does not result in the ignition condition of the tubes of the counting circuit MS being permanently varied.

Assume now that the subscriber being called is not busy. The ignition of the tube B13 then causes the tube BB to become conductive with the third dialling pulse, since the voltage of the cathode of the tube BB is now equal to earth potential. The current flowing through the main discharge path between cathode k and anode a of tube BB causes an increase in the potential of point Q up to 27 volts, so that the subscribers line is marked busy and can no longer be reached by way of another connecting circuit, as has been explained above. Furthermore, the potential of point Q decreases further, so that tube B1 transfers a positive pulse to the point U, which causes ignition of the tubes B4. and B5, so that a subsequent tube in the counting circuit MS ignites, but immediately extinguishes again due to the ignition of tube B5. Since the counting circuit has thus returned to its normal position, the potential of point W is equal to earth potential and rectifier g1 is cut off, so that busy tone is not supplied to the subscriber at station AA. During dialling, busy tone may be supplied to the subscribers station but it cannot be heard-by him, since his apparatus is designed in known manner to be such that the receiver is short-circuited during dialling.

If the subscriber at station AB takes up the receiver to answer the call, the closure of the line loop results in a negative voltage pulse at the point P, which is transferred by way of inductor L1 to the point Q and is further transferred by tube B1 with opposite polarity to the point U. The positive pulse at the point U causes ignition of the tubes B2 and B3 in the manner already described, so that tube B11 becomes conductive and immediately extinguishes again due to the ignition of tube B5. The desired connection betwen the subscribers at stations AA and AB is thus established and intelligence currents may be transmitted in either direction by way of transformer TA, the main discharge paths of tubes BA, BB and transformer TB.

When after the call is over, one of the subscribers replaces down the receiver, a strong positive closing pulse is transferred to the point Q with the result that the tubes BA and BB are extinguished in the manner already described and the circuit returns to its normal condition.

What we claim is:

1. An electronic dialing circuit in automatic signaling system for numerically establishing a connection between one of a plurality of apparatus of a first kind and one of a plurality of apparatus of a second kind comprising a first multipled point coupled with each apparatus of said first kind, a first impedance interposed between said first multipled point and a first terminal of a source of supply, a second multipled point coupled with each apparatus of said second kind, a plurality of gas-filled tubes having ignition electrodes, said tubes being parallelly connected and interposed between said second multipled point and said first multipled point, a second impedance interposed between said second multipled point and a second terminal of said source of supply, the difference in potential between said first and second tenninals of said source of supply being lower than the ignition voltage and higher than the operating voltage of said gas-filled tube, a calling line providing intelligence currents and dialing pulses coupled to said first multipled point, said apparatus of the first kind including an electronic counting circuit having a plurality of output marking points and means coupled to said first multipled point for applying impulses of a determined polarity to said counting circuit, said plurality of output marking points having a voltage which is controlled by said counting circuit as a function of said impulses and a plurality of integrating networks, each of the ignition electrodes of said gas-filled tubes being coupled to one of said integrating networks, said marking points being coupled to the ignition electrodes of said gas-filled tubes through the respective integrating network, said counting circuit having any of a normal condition and a plurality of electrical counting conditions and passing to a subsequent counting condition when one of said impulses is applied to said counting circuit, each counting condition having a voltage at one of said output marking points which is higher than the voltage required to ignite one of said gasfilled tubes when said tubes are inactive.

2. An electronic dialing circuit, as set forth in claim 1, wherein said means for applying impulses includes an amplifier and a pulse limiting circuit coupled thereto.

3. An electronic dialing circuit, as set forth in claim 1, further including means for restoring said counting circuit to its normal condition, said means responding when a pulse of a strength exceeding a predetermined threshold value occurs at said first multipled point, said threshold value being higher than the maximum value of said dialing pulses.

4. An electronic dialing circuit, as set forth in claim 3, wherein said counting circuit comprises a plurality of additional gas-filled tubes and a common impedance coupled to the outputs of said additional tubes and a further gas-filled tube having a control electrode coupled to said first multipled point and an output electrode coupled to said common impedance.

5. An electronic dialing circuit, as set forth in claim 3,

wherein said means for restoring said counting circuit to its normal condition responds to a pulse which occurs at the first multipled point upon ignition of one of said plurality of gas-filled tubes.

6. An electronic dialing circuit, as set forth in claim 1, further including a busy tone generator and a circuit element coupling said generator to said first multipled point, said circuit element being controlled by said counting circuit to provide busy tone to said first multipled point only when said counting circuit has a condition other than the normal condition.

7. An electronic dialing circuit, as set forth in claim 2, further including means coupled to said first multipled point and responsive to a first pulse of opposite polarity to that to which said counting circuit responds, said latter means supplying a second pulse to said first multipled point for extinguishing one of said plurality of gas-filled tubes, said second pulse having the same polarity as that to which said counting circiut responds and having a strength exceeding a predetermined threshold value, said threshold value being higher than the maximum value of said dialing pulses.

8. An electronic dialing circuit, as set forth in claim 7, wherein said latter means includes said amplifier coupled to said first multipled point, a first auxiliary gasfilled tube having a first cathode, a rectifier interposed between said amplifier and said cathode, a second auxiliary gas-filled tube having a second cathode, an ignition electrode coupled to said first cathode and an anode coupled to said first multipled point, and an impedance coupled to the cathodes of each of said auxiliary tubes whereby said auxiliary tubes operate in an unstable manner.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,434,989 Christian Jan. 27, 1948 2,562,100 Holden July 24, 1951 2,598,392 Kaell et al. May 27, 1952 

